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L P Keller - One of the best experts on this subject based on the ideXlab platform.
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the effect of progressive Space Weathering on the organic and inorganic components of a carbonaceous chondrite
Icarus, 2020Co-Authors: M S Thompson, L P Keller, M J Loeffler, R V Morris, R Christoffersen, S J Clemett, D Trang, David G AgrestiAbstract:Abstract We performed pulsed laser irradiation to simulate the progressive Space Weathering of three individual chips of the CM2 Murchison meteorite. After irradiation, we performed two-step laser desorption mass spectrometry to analyze alterations in the concentration, distribution, and functional group chemistry of organics in the samples. These results indicate an increase in the concentration of aromatic organic species in the irradiated regions of the samples compared to the unirradiated areas. We utilized optical reflectance spectroscopy, Fourier-transform infrared spectroscopy, and Mossbauer spectroscopy to investigate changes in the spectral characteristics of the samples as a result of simulated progressive Space Weathering. We observed an overall decrease in reflectance spectra of the irradiated samples. The spectra also exhibit a bluing trend after irradiation, the degree of which weakens with progressive laser exposure. Finally, we used scanning electron microscopy and transmission electron microscopy to examine changes in microstructure and chemistry of the irradiated samples. We observed vesicles and nanoparticles in the melt layers produced by laser irradiation. Our results indicate that the nanoparticle compositions evolve with increasing laser irradiation, progressing from a mineralogically diverse group towards a population dominated by Fe-Ni-sulfides. Radiative transfer models were used to examine the influence of various nanoparticle compositions on sample spectral properties, the results of which indicate nanoparticle size and mineralogy may result in competing spectral effects. We discuss the implications these experiments have for the Space Weathering of primitive, organic-rich asteroids.
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spectral and chemical effects of simulated Space Weathering of the murchison cm2 carbonaceous chondrite
Icarus, 2019Co-Authors: M S Thompson, L P Keller, M J Loeffler, R V Morris, R ChristoffersenAbstract:Abstract We performed pulsed-laser irradiation of a chip of the CM2 Murchison carbonaceous chondrite meteorite to simulate micrometeorite impacts on carbonaceous asteroids. Optical reflectance spectroscopy and transmission electron microscopy were performed to characterize the unirradiated and irradiated samples and vapor and melt deposits collected on a glass slide ∼7 mm from the surface of the sample. The spectrum of the deposit on the glass slide shows a red slope between 0.35–2.5 µm, while the irradiated surface of the meteorite shows only slight darkening over the same spectral range. We identified predominant melt products and vesiculated textures in the glass slide deposit, in the fine-grained matrix of the meteorite, and in individual mineral phases of the meteorite chip. Extracted focused ion beam (FIB) sections from the matrix material, an olivine grain, a pentlandite grain, and from the glass slide deposit were analyzed by scanning transmission electron microscopy (STEM). Microstructural and chemical analyses based on the STEM observations show widespread melting and the formation of Fe-bearing nanoparticles (including prevalent Fe–Ni–sulfides) across the surface of the meteorite. The section extracted from the glass slide revealed nanoparticles embedded in a chemically and microstructurally complex deposit, which likely formed as a result of both melting and vaporization processes. These analyses reveal a significantly more compositionally diverse population of nanoparticles compared to what is observed in lunar or ordinary chondritic Space weathered samples. We discuss the implications these results have for the Space Weathering of carbonaceous asteroids and their importance for understanding the surface processes on primitive bodies.
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Space Weathering Rates in Lunar and Itokawa Samples
2017Co-Authors: E. L. Berger, L P KellerAbstract:Space Weathering alters the chemistry, microstructure, and spectral proper-ties of grains on the surfaces of airless bodies by two major processes: micrometeorite impacts and solar wind interactions. Investigating the nature of Space Weathering processes both in returned samples and in remote sensing observations provides information fundamental to understanding the evolution of airless body regoliths, improving our ability to determine the surface composition of asteroids, and linking meteorites to specific asteroidal parent bodies. Despite decades of research into Space Weathering processes and their effects, we still know very little about Weathering rates. For example, what is the timescale to alter the reflectance spectrum of an ordinary chondrite meteorite to resemble the overall spectral shape and slope from an S-type asteroid? One approach to answering this question has been to determine ages of asteroid families by dynamical modeling and determine the spectral proper-ties of the daughter fragments. However, large differences exist between inferred Space Weathering rates and timescales derived from laboratory experiments, analysis of asteroid family spectra and the Space Weathering styles; estimated timescales range from 5000 years up to 108 years. Vernazza et al. concluded that solar wind interactions dominate asteroid Space Weathering on rapid timescales of 10(exp 4)-10(exp 6) years. Shestopalov et al. suggested that impact-gardening of regolith particles and asteroid resurfacing counteract the rapid progress of solar wind optical maturation of asteroid surfaces and proposed a Space Weathering timescale of 10(exp 5)-10(exp 6) years.
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Plagioclase-Rich Itokawa Grains: Space Weathering, Exposure Ages, and Comparison to Lunar Soil Grains
2017Co-Authors: L P Keller, E. BergeAbstract:Regolith grains returned by the Hayabusa mission to asteroid 25143 Itokawa provide the only samples currently available to study the interaction of chondritic asteroidal material with the Space Weathering environment. Several studies have documented the surface alterations observed on the regolith grains, but most of these studies involved olivine because of its abundance. Here we focus on the rarer Itokawa plagioclase grains, in order to allow comparisons between Itokawa and lunar soil plagioclase grains for which an extensive data set exists.
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agglutinates in howardite nwa 1769 Space Weathering on vesta
Lunar and Planetary Science Conference, 2015Co-Authors: Y Liu, S K Noble, L P Keller, R Christoffersen, A A Fraeman, Z Rahman, B L Ehlman, J A BarratAbstract:A.A. Fraeman3, R. Christoffersen4, Z. Rahman4, B.L. Ehlmann1,3, S.K. Noble5, and J.A. Barrat6. 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA. 2ARES, Mail Code KR, NASA JSC, Houston, TX 77058, USA. 3Div. of Geol. & Planet. Sci., California Institute of Technology, Pasadena, CA 91125, USA. 4Jacobs, NASA JSC, Mail Code XI, Houston, TX 77058, USA. 5. NASA GSFC Mail Code 691, Greenbelt MD 20771. USA. 6Universite de Brest, CNRS UMR 6538 (Domaines Oceaniques), I.U.E.M., Place Nicolas 12 Copernic, 29280 Plouzane, France. (Email: yang.liu@jpl.nasa.gov).
Sho Sasaki - One of the best experts on this subject based on the ideXlab platform.
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spectral decomposition of asteroid itokawa based on principal component analysis
Icarus, 2018Co-Authors: Sumire Koga, T Hiroi, Seiji Sugita, Shunichi Kamata, Masateru Ishiguro, Eri Tatsumi, Sho SasakiAbstract:Abstract The heliocentric stratification of asteroid spectral types may hold important information on the early evolution of the Solar System. Asteroid spectral taxonomy is based largely on principal component analysis. However, how the surface properties of asteroids, such as the composition and age, are projected in the principal-component (PC) Space is not understood well. We decompose multi-band disk-resolved visible spectra of the Itokawa surface with principal component analysis (PCA) in comparison with main-belt asteroids. The obtained distribution of Itokawa spectra projected in the PC Space of main-belt asteroids follows a linear trend linking the Q-type and S-type regions and is consistent with the results of Space-Weathering experiments on ordinary chondrites and olivine, suggesting that this trend may be a Space-Weathering-induced spectral evolution track for S-type asteroids. Comparison with Space-Weathering experiments also yield a short average surface age (
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pulse laser irradiation experiments of murchison cm2 chondrite for reproducing Space Weathering on c type asteroids
Icarus, 2015Co-Authors: Moe Matsuoka, T Hiroi, Tomoki Nakamura, Yuki Kimura, Ryosuke Nakamura, Satoshi Okumura, Sho SasakiAbstract:Abstract We performed pulse-laser irradiation experiments of a primitive meteorite to simulate Space Weathering by micrometeorite bombardments on C-type asteroids. Pellets of powdered Murchison CM2 chondrite were set in vacuum and exposed to pulse laser with a diameter of 0.5 mm and delivered energies of 5, 10, and 15 mJ. We measured reflectance spectra of unirradiated and irradiated surfaces of the pellets. During analysis the pellet was heated to approximately 100 °C and purged in N 2 gas in order to reduce absorption of ambient water. The spectra become darker and bluer with increasing laser energies. Their UV reflectance increases and 0.7- and 3-μm band depths decrease from 0 to 15 mJ. The spectral bluing observed in our experiments reproduces the bluing occurred during Space Weathering of C-type asteroids. High-resolution observation by a transmission electron microscope showed that the laser heating causes preferential melting and evaporation in FeS-rich fine-grained portions, which results in dispersion and deposition of numerous FeS-rich amorphous silicate particles 20–1000 nm in size on the surface of the pellet. In addition, at the laser-irradiated but unmelted areas, heat-induced amorphization and decomposition of serpentine occur. These mineralogical changes make the reflectance spectra of the Murchison CM chondrite darker and bluer.
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production of iron nanoparticles by laser irradiation in a simulation of lunar like Space Weathering
Nature, 2001Co-Authors: Sho Sasaki, K Nakamura, Y Hamabe, E Kurahashi, T HiroiAbstract:‘Space Weathering’ is the term applied to the darkening and reddening of planetary surface materials with time, along with the changes to the depths of absorption bands in their optical spectra. It has been invoked to explain the mismatched spectra of lunar rocks and regolith, and between those of asteroids and meteorites1,2,3,4,5,6. The formation of nanophase iron particles on regolith grains as a result of micrometeorite impacts or irradiation by the solar wind has been proposed as the main cause of the change in the optical properties7,8. But laboratory simulations9,10,11,12,13,14 have not revealed the presence of these particles, although nano-second-pulse laser irradiation did reproduce the optical changes12. Here we report observations by transmission electron microscopy of olivine samples subjected to pulse laser irradiation. We find within the amorphous vapour-deposited rims of olivine grains nanophase iron particles similar to those observed in the rims of Space-weathered lunar regolith grains15,16. Reduction by hydrogen atoms implanted by the solar wind is therefore not necessary to form the particles. Moreover, the results support the idea that ordinary chondrites came from S-type asteroids5, and thereby provides some constraints on the surface exposure ages of those asteroids.
T Hiroi - One of the best experts on this subject based on the ideXlab platform.
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spectral decomposition of asteroid itokawa based on principal component analysis
Icarus, 2018Co-Authors: Sumire Koga, T Hiroi, Seiji Sugita, Shunichi Kamata, Masateru Ishiguro, Eri Tatsumi, Sho SasakiAbstract:Abstract The heliocentric stratification of asteroid spectral types may hold important information on the early evolution of the Solar System. Asteroid spectral taxonomy is based largely on principal component analysis. However, how the surface properties of asteroids, such as the composition and age, are projected in the principal-component (PC) Space is not understood well. We decompose multi-band disk-resolved visible spectra of the Itokawa surface with principal component analysis (PCA) in comparison with main-belt asteroids. The obtained distribution of Itokawa spectra projected in the PC Space of main-belt asteroids follows a linear trend linking the Q-type and S-type regions and is consistent with the results of Space-Weathering experiments on ordinary chondrites and olivine, suggesting that this trend may be a Space-Weathering-induced spectral evolution track for S-type asteroids. Comparison with Space-Weathering experiments also yield a short average surface age (
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pulse laser irradiation experiments of murchison cm2 chondrite for reproducing Space Weathering on c type asteroids
Icarus, 2015Co-Authors: Moe Matsuoka, T Hiroi, Tomoki Nakamura, Yuki Kimura, Ryosuke Nakamura, Satoshi Okumura, Sho SasakiAbstract:Abstract We performed pulse-laser irradiation experiments of a primitive meteorite to simulate Space Weathering by micrometeorite bombardments on C-type asteroids. Pellets of powdered Murchison CM2 chondrite were set in vacuum and exposed to pulse laser with a diameter of 0.5 mm and delivered energies of 5, 10, and 15 mJ. We measured reflectance spectra of unirradiated and irradiated surfaces of the pellets. During analysis the pellet was heated to approximately 100 °C and purged in N 2 gas in order to reduce absorption of ambient water. The spectra become darker and bluer with increasing laser energies. Their UV reflectance increases and 0.7- and 3-μm band depths decrease from 0 to 15 mJ. The spectral bluing observed in our experiments reproduces the bluing occurred during Space Weathering of C-type asteroids. High-resolution observation by a transmission electron microscope showed that the laser heating causes preferential melting and evaporation in FeS-rich fine-grained portions, which results in dispersion and deposition of numerous FeS-rich amorphous silicate particles 20–1000 nm in size on the surface of the pellet. In addition, at the laser-irradiated but unmelted areas, heat-induced amorphization and decomposition of serpentine occur. These mineralogical changes make the reflectance spectra of the Murchison CM chondrite darker and bluer.
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Space Weathering of ordinary chondrite parent bodies its impact on the method of distinguishing h l and ll types and implications for itokawa samples returned by the hayabusa mission
Lunar and Planetary Science Conference, 2011Co-Authors: T Hiroi, S Sasaki, S K Noble, C M PietersAbstract:As the most abundance meteorites in our collections, ordinary chondrites potentially have very important implications on the origin and formation of our Solar System. In order to map the distribution of ordinary chondrite-like asteroids through remote sensing, the Space Weathering effects of ordinary chondrite parent bodies must be addressed through experiments and modeling. Of particular importance is the impact on distinguishing different types (H/L/LL) of ordinary chondrites. In addition, samples of asteroid Itokawa returned by the Hayabusa Spacecraft may re~ veal the mechanism of Space Weathering on an LLchondrite parent body. Results of Space Weathering simulations on ordinary chondrites and implications for Itokawa samples are presented here.
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changes of band i center and band ii band i area ratio in reflectance spectra of olivine pyroxene mixtures due to the Space Weathering and grain size effects
LPI, 2002Co-Authors: Y Ueda, C M Pieters, T Hiroi, M MiyamotoAbstract:Introduction: In the visible and near-infrared wavelength region, reflectance spectrum of olivine and orthopyroxene (opx), which are two of the most common rock-forming minerals, exhibit some characteristic absorption features especially fit for remote sensing. Opx has two absorption bands around 0.9 μm and 2 μm, whereas olivine shows a complex absorption band around 1 μm and no band around 2 μm. Each of the absorption bands of opx consists of a single absorption, and the 1 μm band of olivine is a composite of three [e.g., 1]. The 1 μm band is generally referred to as the “Band I” and the 2 μm band as the “Band II”. One of the methods for estimating the olivine/opx modal abundances from their reflectance spectra is a plot of the Band I center versus Band II/Band I (BII/BI) area ratio [2, 3]. Cloutis et al. [2] estimated the modal abundance from the reflectance spectra of laboratory olivine-opx mixtures using various methods. Gaffey et al. [3] used the Band I center vs. BII/BI area ratio plot and explained the relationship between the S-type asteroids and ordinary chondrites (OCs). Presented here is the possibility that the Space Weathering and grain size effects have significant influence on the Band I center vs. the BII/BI area ratio plot.
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production of iron nanoparticles by laser irradiation in a simulation of lunar like Space Weathering
Nature, 2001Co-Authors: Sho Sasaki, K Nakamura, Y Hamabe, E Kurahashi, T HiroiAbstract:‘Space Weathering’ is the term applied to the darkening and reddening of planetary surface materials with time, along with the changes to the depths of absorption bands in their optical spectra. It has been invoked to explain the mismatched spectra of lunar rocks and regolith, and between those of asteroids and meteorites1,2,3,4,5,6. The formation of nanophase iron particles on regolith grains as a result of micrometeorite impacts or irradiation by the solar wind has been proposed as the main cause of the change in the optical properties7,8. But laboratory simulations9,10,11,12,13,14 have not revealed the presence of these particles, although nano-second-pulse laser irradiation did reproduce the optical changes12. Here we report observations by transmission electron microscopy of olivine samples subjected to pulse laser irradiation. We find within the amorphous vapour-deposited rims of olivine grains nanophase iron particles similar to those observed in the rims of Space-weathered lunar regolith grains15,16. Reduction by hydrogen atoms implanted by the solar wind is therefore not necessary to form the particles. Moreover, the results support the idea that ordinary chondrites came from S-type asteroids5, and thereby provides some constraints on the surface exposure ages of those asteroids.
M J Loeffler - One of the best experts on this subject based on the ideXlab platform.
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the effect of progressive Space Weathering on the organic and inorganic components of a carbonaceous chondrite
Icarus, 2020Co-Authors: M S Thompson, L P Keller, M J Loeffler, R V Morris, R Christoffersen, S J Clemett, D Trang, David G AgrestiAbstract:Abstract We performed pulsed laser irradiation to simulate the progressive Space Weathering of three individual chips of the CM2 Murchison meteorite. After irradiation, we performed two-step laser desorption mass spectrometry to analyze alterations in the concentration, distribution, and functional group chemistry of organics in the samples. These results indicate an increase in the concentration of aromatic organic species in the irradiated regions of the samples compared to the unirradiated areas. We utilized optical reflectance spectroscopy, Fourier-transform infrared spectroscopy, and Mossbauer spectroscopy to investigate changes in the spectral characteristics of the samples as a result of simulated progressive Space Weathering. We observed an overall decrease in reflectance spectra of the irradiated samples. The spectra also exhibit a bluing trend after irradiation, the degree of which weakens with progressive laser exposure. Finally, we used scanning electron microscopy and transmission electron microscopy to examine changes in microstructure and chemistry of the irradiated samples. We observed vesicles and nanoparticles in the melt layers produced by laser irradiation. Our results indicate that the nanoparticle compositions evolve with increasing laser irradiation, progressing from a mineralogically diverse group towards a population dominated by Fe-Ni-sulfides. Radiative transfer models were used to examine the influence of various nanoparticle compositions on sample spectral properties, the results of which indicate nanoparticle size and mineralogy may result in competing spectral effects. We discuss the implications these experiments have for the Space Weathering of primitive, organic-rich asteroids.
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spectral and chemical effects of simulated Space Weathering of the murchison cm2 carbonaceous chondrite
Icarus, 2019Co-Authors: M S Thompson, L P Keller, M J Loeffler, R V Morris, R ChristoffersenAbstract:Abstract We performed pulsed-laser irradiation of a chip of the CM2 Murchison carbonaceous chondrite meteorite to simulate micrometeorite impacts on carbonaceous asteroids. Optical reflectance spectroscopy and transmission electron microscopy were performed to characterize the unirradiated and irradiated samples and vapor and melt deposits collected on a glass slide ∼7 mm from the surface of the sample. The spectrum of the deposit on the glass slide shows a red slope between 0.35–2.5 µm, while the irradiated surface of the meteorite shows only slight darkening over the same spectral range. We identified predominant melt products and vesiculated textures in the glass slide deposit, in the fine-grained matrix of the meteorite, and in individual mineral phases of the meteorite chip. Extracted focused ion beam (FIB) sections from the matrix material, an olivine grain, a pentlandite grain, and from the glass slide deposit were analyzed by scanning transmission electron microscopy (STEM). Microstructural and chemical analyses based on the STEM observations show widespread melting and the formation of Fe-bearing nanoparticles (including prevalent Fe–Ni–sulfides) across the surface of the meteorite. The section extracted from the glass slide revealed nanoparticles embedded in a chemically and microstructurally complex deposit, which likely formed as a result of both melting and vaporization processes. These analyses reveal a significantly more compositionally diverse population of nanoparticles compared to what is observed in lunar or ordinary chondritic Space weathered samples. We discuss the implications these results have for the Space Weathering of carbonaceous asteroids and their importance for understanding the surface processes on primitive bodies.
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irradiation of olivine by 4 kev he simulation of Space Weathering by the solar wind
Journal of Geophysical Research, 2009Co-Authors: M J Loeffler, C A Dukes, R A BaragiolaAbstract:[1] We have studied the effects of 4 keV He+ ion irradiation on olivine while measuring, in situ, changes in the near-infrared (NIR) reflectance and in the chemical composition of the surface. The observed changes in reflectance are reddening and the attenuation of the Fe-3d absorption bands in the NIR. Spectral reddening of irradiated olivine powder (<45 μm) correlates with the amount of metallic iron formed by ion impact, consistent with the idea that Space-Weathering effects in the reflectance of olivine-bearing S type asteroids are due to the formation of metallic iron. The metallization rate of the powder is about half that of a sectioned rock of olivine, which we propose is a consequence of redeposition of sputtered material. The NIR spectral changes observed in ion irradiation experiments are similar to those observed in our previous experiments on vapor redeposition, indicating that different Space Weathering mechanisms can lead to similar final effects on reflectance. Finally, we estimate that at 1 AU the spectral reddening caused by the solar wind saturates approximately 2 orders of magnitude faster than comparable reddening caused by micrometeorite impacts.
C M Pieters - One of the best experts on this subject based on the ideXlab platform.
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Distinctive Space Weathering on Vesta from regolith mixing processes
Nature, 2012Co-Authors: C M Pieters, Brett W. Denevi, D T Blewett, E. Ammannito, M. C. De Sanctis, M. J. Gaffey, L. Le Corre, S. Marchi, T. B. Mccord, L. A. McfaddenAbstract:The surface of the asteroid Vesta has prominent near-infrared absorption bands characteristic of a range of pyroxenes, confirming a direct link to the basaltic howardite–eucrite–diogenite class of meteorites^ 1 , 2 , 3 . Processes active in the Space environment produce ‘Space Weathering’ products that substantially weaken or mask such diagnostic absorption on airless bodies observed elsewhere^ 4 , 5 , and it has long been a mystery why Vesta’s absorption bands are so strong. Analyses of soil samples from both the Moon^ 6 and the asteroid Itokawa^ 7 determined that nanophase metallic particles (commonly nanophase iron) accumulate on the rims of regolith grains with time, accounting for an observed optical degradation. These nanophase particles, believed to be related to solar wind and micrometeoroid bombardment processes, leave unique spectroscopic signatures that can be measured remotely^ 8 , 9 , 10 but require sufficient spatial resolution to discern the geologic context and history of the surface, which has not been achieved for Vesta until now. Here we report that Vesta shows its own form of Space Weathering, which is quite different from that of other airless bodies visited. No evidence is detected on Vesta for accumulation of lunar-like nanophase iron on regolith particles, even though distinct material exposed at several fresh craters becomes gradually masked and fades into the background as the craters age. Instead, spectroscopic data reveal that on Vesta a locally homogenized upper regolith is generated with time through small-scale mixing of diverse surface components. Whereas Space Weathering of some airless bodies, such as the Moon, occurs through the accumulation on regolith of nanophase metallic particles, spectroscopic data show that Space Weathering of the asteroid Vesta occurs through the small-scale mixing of diverse surface components, which gradually generates locally homogenized upper regolith. Between 16 July 2011 and 5 September 2012, NASA's Space probe Dawn was orbiting Vesta, a protoplanet thought to have survived virtually intact since an early phase of Solar System formation. In this issue of Nature , two groups report on the encounter. Carle Pieters and co-workers find that Space Weathering on Vesta has followed a different course from that observed on the Moon and on Itokawa, the asteroid sampled in an Earth-return mission. On Vesta, Weathering involved fine-scale regolith (soil) mixing that has removed clear traces of recent impact deposits. There are no signs of the nanophase metallic-particle deposits seen on the Moon and Itokawa. Thomas McCord and co-authors describe two main types of material on Vesta's surface: bright and dark. The bright material may be uncontaminated indigenous Vesta basaltic soil, with the darker material derived from low-albedo impactors. Dawn has now moved on and is due to rendezvous with the protoplanet Ceres in February 2015.
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optical maturity variation in lunar spectra as measured by moon mineralogy mapper data
Journal of Geophysical Research, 2011Co-Authors: J Nettles, M Staid, S Besse, J Boardman, Roger N Clark, D Dhingra, P Isaacson, R L Klima, G Y Kramer, C M PietersAbstract:[1] High spectral and spatial resolution data from the Moon Mineralogy Mapper (M3) instrument on Chandrayaan-1 are used to investigate in detail changes in the optical properties of lunar materials accompanying Space Weathering. Three spectral parameters were developed and used to quantify spectral effects commonly thought to be associated with increasing optical maturity: an increase in spectral slope (“reddening”), a decrease in albedo (“darkening”), and loss of spectral contrast (decrease in absorption band depth). Small regions of study were defined that sample the ejecta deposits of small fresh craters that contain relatively crystalline (immature) material that grade into local background (mature) soils. Selected craters are small enough that they can be assumed to be of constant composition and thus are useful for evaluating trends in optical maturity. Color composites were also used to identify the most immature material in a region and show that maturity trends can also be identified using regional soil trends. The high resolution M3 data are well suited to quantifying the spectral changes that accompany Space Weathering and are able to capture subtle spectral variations in maturity trends. However, the spectral changes that occur as a function of maturity were observed to be dependent on local composition. Given the complexity of Space Weathering processes, this was not unexpected but poses challenges for absolute measures of optical maturity across diverse lunar terrains.
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Space Weathering of ordinary chondrite parent bodies its impact on the method of distinguishing h l and ll types and implications for itokawa samples returned by the hayabusa mission
Lunar and Planetary Science Conference, 2011Co-Authors: T Hiroi, S Sasaki, S K Noble, C M PietersAbstract:As the most abundance meteorites in our collections, ordinary chondrites potentially have very important implications on the origin and formation of our Solar System. In order to map the distribution of ordinary chondrite-like asteroids through remote sensing, the Space Weathering effects of ordinary chondrite parent bodies must be addressed through experiments and modeling. Of particular importance is the impact on distinguishing different types (H/L/LL) of ordinary chondrites. In addition, samples of asteroid Itokawa returned by the Hayabusa Spacecraft may re~ veal the mechanism of Space Weathering on an LLchondrite parent body. Results of Space Weathering simulations on ordinary chondrites and implications for Itokawa samples are presented here.
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mineralogical and chemical characterization of lunar highland soils insights into the Space Weathering of soils on airless bodies
Journal of Geophysical Research, 2010Co-Authors: Lawrence A Taylor, C M Pieters, L P Keller, Allan Patchen, Donghwa S Taylor, Richard V Morris, David S MckayAbstract:[1] With reflectance spectroscopy, one is measuring only properties of the fine-grained regolith most affected by Space Weathering. The Lunar Soil Characterization Consortium has undertaken the task of coordinated characterization of lunar soils, with respect to their mineralogical and chemical makeup. It is these lunar soils that are being used as “ground truth” for all airless bodies. Modal abundances and chemistries of minerals and glasses in the finest size fractions (20–45, 10–20, and <10 μm) of four Apollo 14 and six Apollo 16 highland soils have been determined, as well as their bulk chemistry and IS/FeO values. Bidirectional reflectance measurements (0.3–2.6 μm) of all samples were performed in the Reflectance Experiment Laboratory. A significant fraction of nanophase Fe0 (np-Fe0) appears to reside in agglutinitic glasses. However, as grain size of a soil decreases, the percentage of total iron present as np-Fe0 increases significantly, whereas the agglutinitic glass content rises only slightly; this is evidence for a large contribution to the IS/FeO values from the surface-correlated nanophase Fe0, particularly in the <10 μm size fraction. The compositions of the agglutinitic glasses in these fine fractions of the highland soils are different from the bulk chemistry of that size; however, compositional trends of the glasses are not the same as those observed for mare soils. It is apparent that the glasses in the highland soils contain chemical components from outside their terrains. It is proposed that the Apollo 16 soils have been adulterated by the addition of impact-transported soil components from surrounding maria.
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changes of band i center and band ii band i area ratio in reflectance spectra of olivine pyroxene mixtures due to the Space Weathering and grain size effects
LPI, 2002Co-Authors: Y Ueda, C M Pieters, T Hiroi, M MiyamotoAbstract:Introduction: In the visible and near-infrared wavelength region, reflectance spectrum of olivine and orthopyroxene (opx), which are two of the most common rock-forming minerals, exhibit some characteristic absorption features especially fit for remote sensing. Opx has two absorption bands around 0.9 μm and 2 μm, whereas olivine shows a complex absorption band around 1 μm and no band around 2 μm. Each of the absorption bands of opx consists of a single absorption, and the 1 μm band of olivine is a composite of three [e.g., 1]. The 1 μm band is generally referred to as the “Band I” and the 2 μm band as the “Band II”. One of the methods for estimating the olivine/opx modal abundances from their reflectance spectra is a plot of the Band I center versus Band II/Band I (BII/BI) area ratio [2, 3]. Cloutis et al. [2] estimated the modal abundance from the reflectance spectra of laboratory olivine-opx mixtures using various methods. Gaffey et al. [3] used the Band I center vs. BII/BI area ratio plot and explained the relationship between the S-type asteroids and ordinary chondrites (OCs). Presented here is the possibility that the Space Weathering and grain size effects have significant influence on the Band I center vs. the BII/BI area ratio plot.
